Semiconductor laser apparatus

ABSTRACT

A semiconductor laser apparatus includes a semiconductor laser element, a lead frame on which the semiconductor laser element is mounted, and an enclosure attached to the lead frame. When a direction in which a main beam is emitted from the semiconductor laser element is defined as forward, the lead frame has a reference surface serving as a reference for the semiconductor laser element in a forward or backward direction of the main beam, behind a portion where the semiconductor element is mounted.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims benefit of priority under 35USC 119 from the Japanese Patent Application No. 2002-91521, filed onMar. 28, 2002, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor laser apparatus.

Recently, a semiconductor laser apparatus which irradiates the surfaceof an optical disk with a laser beam is widely used in a DVD (DigitalVersatile Disc) system and the like. FIGS. 4A to 4C illustrate thearrangement of a conventional semiconductor laser apparatus. FIG. 4A isa plan view showing the apparatus. FIG. 4B is a longitudinal sectionalview taken along a line C—C in FIG. 4A. FIG. 4C is a left side view.

A semiconductor laser element 103 is mounted on a substrate 105 which ismade of silicon or the like and on which a semiconductor laser elementmounting bed and a light receiving element 104 are formed. Thissemiconductor laser element 103 emits a main laser beam 108 forward (tothe left in FIG. 4A), and emits a monitoring beam 109 backward. Thelight receiving element 104 formed in the surface of the substrate 105receives this monitoring beam 109.

The semiconductor laser element 103 is connected to a lead frame 101 bya bonding wire 107 a. The light receiving element 104 is connected to alead 101 a separated from the lead frame 101 by a bonding wire 107 b.The substrate 105 is connected to a lead 101 b by a bonding wire 107 c.

In addition, an enclosure 102 made of a material such as resin is formedon the lead frame 101 so as to surround the rear portion and two sideportions of the semiconductor laser element 103. An enclosure 102 a isformed on the lower surface of the lead frame 101.

This semiconductor laser apparatus is installed in a hole formed in aholder of a pickup head (not shown). In this installation, a frontsection 201 of the lead frame 101 functions as a reference surface forpositioning in the forward or backward direction of the main laser beam108 (in the horizontal direction in FIG. 4A), and side sections 202function as reference surfaces for positioning in the lateral direction(in the vertical direction in FIG. 4A).

Unfortunately, the above apparatus has the following problem. When thesemiconductor laser apparatus is installed in the holder of the pickuphead, the relative positional relationship between the semiconductorlaser element 103 and the holder is important. That is, the frontsection 201 as the reference in the forward or backward direction of themain laser beam 108 and the semiconductor laser element 103 are insubstantially the same position as shown in FIG. 4A. Therefore, therelative positional relationship between them is unconditionallydetermined, so the degree of freedom of design is very low. This degreeof freedom of design may be increased by moving the semiconductor laserelement 103 backward (to the right in FIG. 4A) as needed. However, thisincreases the dimension in the forward or backward direction of theentire apparatus and hence increases the size of the apparatus, so it isundesirable to use this method.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a semiconductor laserapparatus comprises a semiconductor laser element, a lead frame on whichthe semiconductor laser element is mounted, and an enclosure attached tothe lead frame, wherein when a direction in which a main beam is emittedfrom the semiconductor laser element is defined as forward, the leadframe has a reference surface serving as a reference for thesemiconductor laser element in a forward or backward direction of themain beam, behind a portion where the semiconductor element is mounted.

According to another aspect of the invention, a semiconductor laserapparatus includes a semiconductor laser element, a lead frame on whichthe semiconductor laser element is mounted, an enclosure attached to thelead frame, and a heat sink attached to the enclosure to radiate heatgenerated by the semiconductor laser element, wherein when a directionin which a main beam is emitted from the semiconductor laser element isdefined as forward, the heat sink has a reference surface serving as areference for the semiconductor laser element in the forward or backwarddirection of the main beam, and, when a direction perpendicular to theforward or backward direction of the main beam and parallel to a surfaceof said lead frame on which said semiconductor laser element is mountedis defined as a lateral direction, the heat sink has a reference surfaceserving as a reference for the semiconductor laser element in thelateral direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are a plan view, longitudinal sectional view, andside view, respectively, showing the arrangement of a semiconductorlaser apparatus according to the first embodiment of the presentinvention;

FIGS. 2A, 2B, and 2C are perspective views showing a method of attachinga cover to an enclosure by hot caulking in the semiconductor laserapparatus in order of steps;

FIGS. 3A, 3B, and 3C are a plan view, longitudinal sectional view, andside view, respectively, showing the arrangement of a semiconductorlaser apparatus according to the second embodiment of the presentinvention; and

FIGS. 4A, 4B, and 4C are a plan view, longitudinal sectional view, andside view, respectively, showing the arrangement of a conventionalsemiconductor laser apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to the accompanying drawings.

(1) First Embodiment

FIGS. 1A, 1B, and 1C illustrate the arrangement of a semiconductor laserapparatus according to the first embodiment of the present invention.FIG. 1A is a plan view showing the state in which a cover 2 a of anenclosure 2 of this apparatus is removed. FIG. 1B is a longitudinalsectional view taken along a line A—A in FIG. 1A. FIG. 1C is a sidesectional view.

A semiconductor laser element 3 is mounted on a substrate 6 made of amaterial such as ceramic, and this substrate 6 and a semiconductorsubstrate 4 are mounted on a lead frame 1. The semiconductor laserelement 3 emits a main laser beam 8 forward (to the left in FIG. 1A),and also emits a monitoring beam 9 backward. A light receiving element(not shown) is formed in the surface of the semiconductor substrate 4.This light receiving element receives a reflected beam 9 a formed whenthe monitoring beam 9 is reflected by a light reflecting surface 10formed on the cover 2 a of the enclosure 2.

The semiconductor laser element 3 is connected to the lead frame 1 by abonding wire 7 a. The light receiving element is connected to a lead 1 bseparated from the lead frame 1 by a bonding wire 7 c. The substrate 6is connected to a lead 1 a by a bonding wire 7 b, and to a lead 1 c by abonding wire 7 d.

The enclosure 2 made of a material such as resin is placed on the leadframe 1 so as to surround the rear portion, two side surfaces, and uppersurface, except for the front portion, of the semiconductor laserelement 3 mounted on the lead frame 1.

This semiconductor laser apparatus is installed in a hole formed in aholder of a pickup head (not shown). In this installation, assuming thata direction in which the main beam 8 is emitted from the semiconductorlaser element 3 is forward, front sections 301 of notches formed in thelead frame 1 function as reference surfaces for positioning in theforward or backward direction of the main beam 8 (in the horizontaldirection in FIG. 1A). Also, assuming that a direction perpendicular tothe longitudinal direction and parallel to that surface of the leadframe 1, on which the semiconductor laser element 3 is mounted is thelateral direction, side sections 302 function as reference surfaces forpositioning in this lateral direction (in the vertical direction in FIG.1A). In addition, assuming that a direction perpendicular to thatsurface of the lead frame 1, on which the semiconductor laser element 3is mounted is the vertical direction, and that this surface on which thesemiconductor laser element 3 is mounted is the top surface of the leadframe 1, the bottom surface of the lead frame 1 is a reference surfacein the vertical direction.

In this embodiment as described above, the front sections 301 as thereferences in the forward or backward direction are positioned after (tothe right in FIG. 1A) the semiconductor laser element 3. A relativedistance X1 between the front sections 301 and the semiconductor laserelement 3 can be set to a desired value. This greatly improves thedegree of freedom of design pertaining to the relative distance betweenthe holder and the semiconductor laser element 3 when the semiconductorlaser apparatus is installed in the holder. Also, the bottom surface ofthe lead frame 1 is the reference surface in the vertical direction.This realizes installation with higher accuracy than when the apparatusshown in FIGS. 4A to 4C in which the bottom surface of the lead frame iscovered with an enclosure is installed.

A procedure of fabricating this apparatus will be explained below.First, on a lead frame 1 pressed and molded into a desired pattern, aresin serving as an enclosure 2 is formed by injection molding so as tosurround a portion where a semiconductor laser element 3 is to bemounted. The material of the lead frame 1 is, e.g., a copper-basedmaterial in order to improve the heat radiation properties in operation.However, it is sometimes also possible to use an iron-based materialsuch as a 42 alloy. To improve the ease of assembly, appropriate platingsuch as gold, nickel, or palladium plating can be formed on the leadframe 1 in advance.

Next, a semiconductor substrate 4 in which a light receiving element isformed and a substrate 6 on which the semiconductor laser element 3 ismounted are mounted on the molded lead frame 1. The substrate 6 is madeof, e.g., a ceramic material of aluminum nitride having a thermalexpansion coefficient close to that of the semiconductor laser element3, and having thermal conductivity higher than that of silicon. Anelectrode is formed on the surface of this substrate 6 beforehand bydepositing and patterning an electrode material such as gold.

When the semiconductor substrate 4 and substrate 6 are mounted on thelead frame 1, conduction is ensured by adhering an adhesive such asgold-tin solder by melting it at a temperature of about 300° C.Alternatively, a silver epoxy adhesive or the like can be used insteadof the solder.

The bottom surface of the lead frame 1 is not covered with the enclosure2 but exposed, in order to improve the heat radiation properties whenthe adhesive is heated or the apparatus is installed in the holder. Thelead frame 1 is desirably exposed particularly in that portion of thelead frame 1, which corresponds to a portion where the semiconductorlaser element 3 or the light receiving element of the semiconductorsubstrate 4 is mounted on the opposite side of this lead frame 1.

The apparatus shown in FIGS. 4A to 4C has no good heat radiationproperties, since the bottom surface of the lead frame 101 is coveredwith the portion 102 a of the enclosure 102. By contrast, in theapparatus of this embodiment, the bottom surface of the lead frame 1 isnot covered with the enclosure 2 but exposed. Accordingly, when thisapparatus is installed in a holder of a pickup head, the bottom surfaceof the lead frame 1 is in direct contact with the holder. This improvesthe heat radiation properties because heat generated from thesemiconductor laser element 3 is radiated to the outside via the leadframe 1 and holder.

On the top surface of the lead frame 1, the light receiving elementformed in the surface of the semiconductor substrate 4 is mounted on aplane parallel to the semiconductor laser element 3. This is to improvethe workability and productivity in a series of steps such as a hoopline in which the lead frame flows. The semiconductor laser element 3and semiconductor substrate 4 are adhered by heat onto this molded leadframe 1. Since this heating process is performed, a material such asheat-resistant engineering plastic (e.g., PPA) or a liquid crystalpolymer is used as the enclosure 2. The enclosure 2 can also be made ofa material such as PSF, PES, PPS, PEEK, PAR, PAI, PEI, PI, or FR (PTFE).However, it is favorable to totally take account of, e.g., the heatresistance, chemical resistance, mechanical strength, lead adhesion,moldability, outgas, and cost. Therefore, PPA is used in thisembodiment.

To make electrical connections, the semiconductor laser element 3,semiconductor substrate 4, and substrate 6 are connected to the leadframe 1 or leads 1 a to 1 c by bonding wires 7 a to 7 d.

To downsize the apparatus, the bonding space on the lead frame 1 isconsiderably limited. Especially in the apparatus of this embodimentwhich includes the two-wavelength semiconductor laser element 3 whichemits two different wavelengths, the number of bonding wires increasesaccordingly, so it is important to ensure the bonding space. Inparticular, one end of the wire 7 a having the other end connected tothe semiconductor laser element 3 must be bonded onto the lead frame 1such that this wire 7 a is not brought into contact with the substrate6. However, if the loop of the wire is bent midway along the wire, theassembly yield and assembly speed lower. Therefore, in this embodimentas shown in FIGS. 1A and 1B, a bonding space for connecting the otherend of the wire 7 a is formed before the mounting position of thesubstrate 6 on the lead frame 1.

This makes it possible to shorten the loop of the wire 7 a and form thiswire 7 a into a relatively linear simple shape, thereby improving theease of assembly.

On the other hand, the laser beam emission point of the semiconductorlaser element 3 is positioned after (to the right in FIGS. 1A and 1B)the front end portion of the lead frame 1. Accordingly, to preventadverse effects such as interference caused if the laser beam isintercepted by the front end portion of the lead frame 1, a window 303is formed by notching a portion of the lead frame 1 before the regionwhere the semiconductor laser element 3 is mounted, thereby preventinginconvenience.

The semiconductor laser element 3 and semiconductor substrate 4 can beplaced on the lead frame 1 by using the window 303 as a reference whenthe semiconductor laser element 3 is mounted. Especially when aplurality of laser beams are emitted from one semiconductor laserelement 3 as in this embodiment, the semiconductor laser element 3 mustbe placed in alignment with the electrode pattern on the substrate 6.Therefore, the substrate 6 must be accurately placed on the lead frame1, so confirmation of the mounting position is important.

After the apparatus is completely assembled as described above, a cover2 a is accurately adhered to the body of the enclosure 2 by an adhesiveor by hot welding, ultrasonic welding, press fit, fitting, or the like.For example, the adhesion surface is coated with a silicone-basedadhesive, and the cover 2 a is attached to the enclosure 2 and adheredby curing the adhesive at about 200° C. As described above, the lightreflecting surface 10 is formed on a portion of the inner surface ofthis cover 2 a, so the monitoring beam 9 emitted backward from thesemiconductor laser element 3 is reflected and fed into the lightreceiving element. Accordingly, the material and surface treatment ofthe cover 2 a must be so selected as to increase the light reflectanceof this light reflecting surface 10.

In this embodiment, PPA is used as the material of this cover 2 asimilar to the body of the enclosure 2, by taking not only an adhesivebut also ultrasonic welding or hot welding into consideration. Asanother material, plated PBT, metal, or resin can also be used as thecover 2 a. Similar to the lead frame 1, a notch can also be formed inthe top surface of the cover 2 a so as not to intercept the main laserbeam 8 from the semiconductor laser element 3.

Alternatively, a method so-called hot caulking can also be used. Thatis, one or a plurality of projections are formed on the body of theenclosure 2, and holes corresponding to these projections are formed inthe cover 2 a. After fitting, the tips of the projections are crushedwith heat and pressure, thereby fixing the cover 2 a to the body of theenclosure 2.

This method will be explained with reference to FIGS. 2A to 2C.

As shown in FIG. 2A, holes 401 are formed in a cover 400. As shown inFIG. 2B, projections 411 are formed on the surface of an enclosure 410.A substrate 412 is mounted on a lead frame 416 which is connected toleads 415 by wires (not shown), and a semiconductor element for emittinga laser beam is mounted on the surface of this substrate 412. The laserbeam is received by a light receiving element formed in a semiconductorsubstrate 414. The enclosure 410 is formed in the surface of the leadframe 416.

As shown in FIG. 2C, the cover 400 can be accurately fixed to theenclosure 410 if the projections and holes are formed with desiredaccuracy. When the projections 411 are made of, e.g., PPA, sufficientfixing strength can be obtained by crushing these projections 411 byheating them to about 150° C. to 300° C. As a cover which is notdirectly heated or processed, it is possible to widely select a materialhaving a relatively low heat resistance or a metal material other thanplastic.

When hot caulking is used as described above, the process can besimplified and the material cost can be saved because no adhesivematerial is used. In addition, there is no adverse effect oncharacteristics, such as impurity adhesion to the semiconductor laserelement or optical system.

Referring to FIGS. 1A to 1C, when a plurality of elements (in thisembodiment, the semiconductor laser element 3 and light receivingelement) are mounted on the lead frame 1, the number of leads increases.Therefore, the lead frame 1 and the leads 1 a to 1 c are cut apart.

As shown in FIG. 1A, this apparatus has a narrow front half and widerear half bounded by the front sections 301 formed in the notches as thereference surfaces in the forward or backward direction of the main beam8. An insertion hole corresponding to the narrow front half of thissemiconductor laser apparatus is formed in a holder of a pickup in whichthe apparatus is installed. The laser apparatus is installed as it isinserted into this hole.

The installation accuracy of the semiconductor laser apparatus hassignificant influence on the performance of the pickup head and the likein which the apparatus is installed. In this embodiment as describedabove, therefore, the side sections 302 of the notches in the lead frame1 are used as the reference surfaces for positioning in the lateraldirection. However, the reference surfaces are not restricted to thesenotched end faces (sections). The area of the reference surfaces can beincreased by using portions other than sections as the referencesurfaces by, e.g., bending the end faces.

As described above, those front sections 301 of the notches in the leadframe 1, which are steps produced between the narrow portion and wideportion are used as the reference surfaces for positioning in theforward or backward direction. When this apparatus is inserted into aholder hole, therefore, the apparatus can be positioned in the forwardor backward direction because these reference surfaces (front sections301) abut against the inner surface of the holder. It is also possibleto form projections on these positioning reference surfaces, and set thetips of these projections as reference positions. Alternatively, aportion other than the lead frame 1, e.g., a portion of the enclosure 2can be set as a reference for positioning in the forward or backwarddirection.

(2) Second Embodiment

A semiconductor laser apparatus according to the second embodiment ofthe present invention will be described below. FIGS. 3A to 3C illustratethe arrangement of this semiconductor laser apparatus. FIG. 3A is a planview showing the state in which a cover 2 a of an enclosure 2 of thisapparatus is removed. FIG. 3B is a longitudinal sectional view takenalong a line A—A in FIG. 3A. FIG. 3C is a left side view. The samereference numerals as in the first embodiment shown in FIGS. 1A to 1Cdenote the same components in FIGS. 3A to 3C, and a detailed explanationthereof will be omitted.

In this embodiment, a heat sink 11 is added to the apparatus accordingto the first embodiment. By attaching this heat sink 11 to a lead frame1, heat generated from a semiconductor laser element 3 can be radiatedto the outside more efficiently.

It is also possible to increase the strength when this apparatus isinstalled in a holder of a pickup head. When the semiconductor laserapparatus shown in FIGS. 4A to 4C is installed in a holder by press fit,those front section 201 and side sections 202 of the lead frame 101,which function as reference surfaces for positioning undergo largepressure and stress. To prevent deformation by such external forces,therefore, the thickness of the lead frame 101 must be increased to someextent, and its material is also largely limited.

By contrast, in this embodiment, assuming that a direction perpendicularto a direction in which a main beam 8 is emitted from the semiconductorlaser element 3 is the lateral direction, arcuate side surfaces 112 ofthe heat sink 11 are used as reference surfaces for positioning in thislateral direction. In addition, a front surface 111 of the heat sink 11is used as a reference surface in the forward or backward direction ofthe main beam 8. Accordingly, even when the apparatus is installed in aholder, the large-area surfaces 111 and 112 of the heat sink 11 receivepressure and stress. So, sufficient strength can be ensured withoutincreasing the thickness of the lead frame 1.

Furthermore, in the structure as shown in FIGS. 4A to 4C, a heat sinkfor improving the heat radiation properties is difficult to attach withhigh accuracy.

In this embodiment, notches are formed in the lead frame 1 as in theabove first embodiment. The heat sink 11 is attached to abut againstfront sections 301 as reference surfaces for positioning in the forwardor backward direction, and side sections 302 as reference surfaces forpositioning in the lateral direction, in these notches. Consequently,the heat sink 11 can be easily and accurately attached to the lead frame1.

To improve the heat radiation properties, a metal material such as acopper- or iron-based material is used as the material of the heat sink11. However, if no superior heat radiation properties are necessary,another material such as plastic can also be used.

The shape of the heat sink 11 of this embodiment is obtained by linearlycutting a lower end 114 and upper end 115 of a disk having apredetermined thickness. The side surfaces 112 of this heat sink 11 arearcuate as they are formed by portions of a cylindrical surface. Acentral axis P of the arcs of these side surfaces 112 is positioned nearthe emission position of the main laser beam 8 from the semiconductorlaser element 3, and so set as to be substantially parallel to theemission direction.

A round hole is formed in a holder in which this apparatus is installed,and the apparatus is inserted such that the arcuate side surfaces 112 ofthe heat sink 11 come in close contact with the inner surface of theround hole. In this manner, the emission direction of the main laserbeam 8 is easily and accurately determined. Also, since the apparatus isinserted into a round hole, positioning in a direction perpendicular tothe main laser beam 8 can be easily performed by the lower end 114 andupper end 115. It is also readily possible to adjust the rotationaldirection of the apparatus after it is inserted.

The lower end 114 and upper end 115 of the heat sink 11 are cut to makethe semiconductor laser apparatus compact, and allow installation in alow-profile pickup head or the like. Since the apparatus according tothe first embodiment described above can be made thin, the apparatus ofthis embodiment in which the heat sink 11 is added to the apparatus ofthe first embodiment can also be made thin. Furthermore, the verticaldimension and shape of the heat sink 11 can be freely designed inaccordance with the design of a pickup head. However, if the apparatusis to be installed in a normal pickup head which is not a low-profilehead, the upper and lower ends of the heat sink 11 need not be cut off.

A notch 116 for accommodating the lead frame 1 and the like is formed ina portion of the heat sink 11. Also, as described above with referenceto FIG. 3C, the emission position of the main laser beam 8 from thesemiconductor laser element 3 is so set as to be aligned with thecentral axis P of the arcuate side surfaces 112 of the heat sink 11.This is to allow the beam emission point of the semiconductor laserelement 3 to always come to a predetermined position, in order to adjustthe rotational direction when this apparatus is installed in a holder ofa pickup head. In addition, the front surface 111 of the heat sink 11 isperpendicular to the side surfaces 112, and part or the whole of thissurface 111 is a reference surface for positioning in the forward orbackward direction of the main beam 8.

In this embodiment, the side surfaces 112 and front surface 111 aredirectly used as the reference surfaces. However, reference portions canalso be additionally formed on these surfaces 111 and 112. For example,it is possible to form projections on the side surfaces 112 and/or thefront surface 111, and use the tips of these projections as referencepositions. In this case, the apparatus is positioned by abutting thesetips of the projections against the inner wall of a hole in a holder.

The heat sink 11 is desirably attached to the lead frame 1 such thatthis heat sink 11 is thermally cemented to or brought into contact witha portion near the surface, or the surface itself, just behind thatportion of the lead frame 1, on which the semiconductor laser element 3is mounted. This improves the heat radiation properties. In thisembodiment, a projection 113 of the heat sink 11 is cemented to thesurface just behind the portion on which the semiconductor laser element3 is mounted. As shown in FIG. 3C, this projection 113 preferably has adimension not extending to the outside from a diameter D of the arcuateside surfaces 112. Accordingly, the apparatus can be installed in aholder while being kept compact in size.

The heat sink 11 can be fixed to the lead frame 1 by, e.g., solder,silver epoxy, or silver brazing. However, this fixing can also beperformed by using an adhesive or grease, or by simple contact bonding,while the heat radiation properties are assured. Consequently, heatgenerated from the semiconductor laser element 3 is radiated to theoutside via the lead frame 1, heat sink 11, and the holder in which thisapparatus is installed.

Each of the above embodiments is merely an example and hence does notrestrict the present invention. For example, in each of the first andsecond embodiments described above, a light receiving element is mountedin addition to a semiconductor laser element. However, the presentinvention is applicable to an apparatus on which no element other than asemiconductor laser element is mounted, or to an apparatus on whichanother element is mounted in addition to a semiconductor laser elementand light receiving element. In addition, the materials of theindividual components can be freely selected as needed.

Furthermore, in the second embodiment, reference surfaces serving asreferences for a semiconductor laser element in the forward or backwarddirection are formed on the heat sink behind a portion where thesemiconductor laser element is mounted. However, depending on the shapeor the like of a holder of a pickup head, reference surfaces serving asreferences in the forward or backward direction can also be formed insubstantially the same position in the forward or backward direction asthe emission position of the main beam 8 from the semiconductor laserelement 3. That is, reference surfaces in the forward or backwarddirection need only be formed on the heat sink in accordance with theshape or the like of a holder, at substantially the same position as theemission position of the main beam 8 of the semiconductor laser element3 or after the emission position.

In the semiconductor laser apparatus of the present invention accordingto each embodiment as has been explained above, the lead frame hasreference surfaces serving as references for a semiconductor laserelement in the forward or backward direction after a portion where thissemiconductor laser element is mounted. Therefore, it is possible toincrease the degree of freedom of design for positioning when thisapparatus is installed in a holder or the like.

Also, when the apparatus includes a heat sink, this heat sink receivesthe stress upon installation instead of the lead frame. This eliminatesthe need to increase the strength of the lead frame, and ensures thestrength upon installation without imposing any limitations on thematerial, thickness, and the like of the lead frame.

1. A semiconductor laser apparatus comprising a semiconductor laserelement, a lead frame on which said semiconductor laser element ismounted, and an enclosure attached to said lead frame, wherein when adirection in which a main beam is emitted from said semiconductor laserelement is defined as forward, said lead frame has a reference surfaceserving as a reference for said semiconductor laser element in a forwardor backward direction of the main beam, and the reference surface isprovided behind a front surface of said semiconductor laser elementemitting the main beam.
 2. An apparatus according to claim 1, furthercomprising a reference surface serving as a reference for saidsemiconductor laser element in a lateral direction, when a directionperpendicular to the longitudinal direction and parallel to a surface ofsaid lead frame, on which said semiconductor laser element is mounted isdefined as the lateral direction.
 3. An apparatus according to claim 2,wherein said enclosure has a window for extracting the beam emitted fromsaid semiconductor laser element forward.
 4. An apparatus according toclaim 2, wherein the reference surface serving as the reference in theforward or backward direction of the main beam is formed in a notch ofsaid lead frame.
 5. An apparatus according to claim 2, wherein thereference surface serving as the reference in the lateral direction is aside surface of said lead frame, and the side surface is perpendicularto the surface of said lead frame, on which said semiconductor laserelement is mounted, and is formed before the reference surface servingas the reference in the forward or backward direction of the main beam.6. An apparatus according to claim 1, wherein when a directionperpendicular to a surface of said lead frame, on which saidsemiconductor laser element is mounted is defined as a verticaldirection, and the mounting surface of said semiconductor laser elementis the top surface of said lead frame, the bottom surface of said leadframe is used as a reference for said semiconductor laser element in thevertical direction.
 7. An apparatus according to claim 6, wherein thebottom surface of said lead frame is exposed from said enclosure.
 8. Anapparatus according to claim 6, wherein said enclosure has a window forextracting the beam emitted from said semiconductor laser elementforward.
 9. An apparatus according to claim 6, wherein the referencesurface serving as the reference in the forward or backward direction ofthe main beam is formed in a notch of said lead frame.
 10. Asemiconductor laser apparatus comprising a semiconductor laser element,a lead frame on which said semiconductor laser element is mounted, andan enclosure and heat sink attached to said lead frame, wherein when adirection in which a main beam is emitted from said semiconductor laserelement is defined as forward, said heat sink has a reference surfaceserving as a reference for said semiconductor laser element in theforward or backward direction of the main beam, and the referencesurface is provided behind a front surface of said semiconductor laserelement emitting the main beam and, when a direction perpendicular tothe forward or backward direction of the main beam and parallel to asurface of said lead frame on which said semiconductor laser element ismounted is defined as a lateral direction, said heat sink has areference surface serving as a reference for said semiconductor laserelement in the lateral direction.
 11. An apparatus according to claim10, wherein a side surface of said heat sink parallel to the forward orbackward direction of the main beam has an arcuate shape and correspondsto the reference surface serving as the reference for said semiconductorlaser element in the lateral direction, a surface of said heat sinkperpendicular to the forward or backward direction of the main beamcorresponds to the reference surface serving as the reference for saidsemiconductor laser element in the longitudinal direction, a centralaxis of the arcuate shape of the side surface is substantially parallelto the emission direction of the main beam from said semiconductor laserelement, and when that surface of said lead frame, on which saidsemiconductor laser element is mounted is defined as a top surface ofsaid lead frame, on a bottom surface of said lead frame a portioncorresponding to the back side of the mounting position of saidsemiconductor laser element or a nearby portion of the portioncorresponding to the back side is in contact with said heat sink.
 12. Anapparatus according to claim 11, wherein said heat sink has a projectionbefore the reference surface serving as the reference in the forward orbackward direction of the main beam, and on the bottom surface of saidlead frame this projection is in contact with the portion correspondingto the back side of the mounting position of said semiconductor laserelement.
 13. An apparatus according to claim 11, wherein said heat sinkhas upper and lower surfaces parallel to the central axis of the arcuateshape of the side surface, and separated by a distance smaller than thediameter of the arc.
 14. An apparatus according to claim 10, whereinsaid heat sink has upper and lower surfaces parallel to the central axisof the arcuate shape of the side surface, and separated by a distancesmaller than a diameter of the arc.
 15. An apparatus according to claim10, wherein a side surface of said heat sink parallel to thelongitudinal direction has an arcuate shape and corresponds to thereference surface serving as the reference for said semiconductor laserelement in the lateral direction, a surface of said heat sinkperpendicular to the longitudinal direction corresponds to the referencesurface serving as the reference for said semiconductor laser element inthe forward or backward direction of the main beam, a central axis ofthe arcuate shape of the side surface is substantially parallel to theemission direction of the main beam from said semiconductor laserelement, and when that surface of said lead frame, on which saidsemiconductor laser element is mounted is defined as a top surface ofsaid lead frame, on a bottom surface of said lead frame a portioncorresponding to the back side of the mounting position of saidsemiconductor laser element or a nearby portion of the portioncorresponding to the back side is in contact with said heat sink.
 16. Anapparatus according to claim 15, wherein said heat sink has a projectionbefore the reference surface serving as the reference in the forward orbackward direction of the main beam, and on the bottom surface of saidlead frame this projection is in contact with the portion correspondingto the back side of the mounting position of said semiconductor laserelement.
 17. An apparatus according to claim 15, wherein said heat sinkhas upper and lower surfaces parallel to the central axis of the arcuateshape of the side surface, and separated by a distance smaller than thediameter of the arc.
 18. An apparatus according to claim 10, whereinsaid heat sink has upper and lower surfaces parallel to the central axisof the arc of the side surface, and separated by a distance smaller thanthe diameter of the arc.
 19. An apparatus according to claim 10, whereina portion of said semiconductor laser apparatus before the referencesurface serving as the reference in the forward or backward direction ofthe main beam has a shape and dimension within the range of a cylinderhaving the same central axis and same diameter as those of the arc ofthe side surface.
 20. A semiconductor laser apparatus comprising asemiconductor laser element, a lead frame on which said semiconductorlaser element is mounted, and an enclosure attached to said lead frame,wherein when a direction in which a main beam is emitted from saidsemiconductor laser element is defined as forward, said lead frame hasnotches having front sections located behind a front surface of saidsemiconductor laser element emitting the main beam, the front sectionsof said notches serve as a reference for said semiconductor laserelement in a forward or backward direction of the main beam when saidsemiconductor laser apparatus is installed in a holder.
 21. An apparatusaccording to claim 20, wherein the front sections of said notches areparallel to the front surface of said semiconductor laser elementemitting the main beam.
 22. An apparatus according to claim 20, whereinsaid notches are not covered with said enclosure.